So, it could be a few things:
1. We just updated to a new version of our upstream forum software. While there isn't a report of this being an issue, they could've messed up notifications.
2. It could be a system/database issue. To address that possibility I just ran database maintenance and rebooted the server. I didn't see anything that pointed to corruption, but better safe than sorry.
My hope is that maintenance will magically cure whatever it was that caused this, but most likely we'll never know why this happened unless we find out it's a bug with the